The issues of authentication and counterfeit deterrence can be important in many contexts. Bills of currency, stock and bond certificates, credit cards, passports, bills of lading, as well as many other legal documents (e.g., deeds, wills, etc.) all must be reliably authentic to be useful.
It is typically important, for an efficient stream of commerce, for bills and certificates to be self-authenticating; that is, for a recipient to be able to determine the authenticity of the document, without resort to extrinsic information, upon presentation. Likewise, it also remains useful for additional tools to be available for a forensic analysis of authenticity, especially covert features which might be missed by even a skilled counterfeiter.
In the realm of currency, anti-counterfeiting methods have become quite sophisticated—the use of two-dimensional authentication mechanisms such as watermarks or special threads incorporated within the paper itself are helpful. However, they remain vulnerable to reverse-engineering. Once a potential counterfeiter learns how to emulate the anti-counterfeiting technology, he may use it to his own advantage. Therefore, the simple release of anti-counterfeiting technology into the world can be an indirect pathway to advance the state of criminal technology.
Several methods have been proposed for increasing the security of paper-based certificates. For example, randomly placed fibers are difficult to counterfeit, so that a coding of location and fiber properties becomes a useful scheme. See, U.S. Pat. Nos. 5,974,150, 6,246,061 and 6,035,914, expressly incorporated herein by reference in their entirety. This coding may be provided in an external database, for example indexed through a serial number, which allows an on-line authentication of a bill. The coding may also be cryptographically printed on the bill, which may allow self-authentication by relying on the cryptographic security. As with all cryptographic schemes, once the scheme is “broken”, than is, a counterfeiter has available to it the tools to read the information encrypted, and/or create a new code which appears legitimate, the cryptographic scheme no longer serves its purpose.
Therefore, it is useful to provide various types or levels of cryptographic authentication to preserve the value of the authentication feature. Advantageously, both physical and algorithmic impediments are presented, increasing the required skill set of the counterfeiter to achieve a successful counterfeit, and also increasing the costs and risks associated with the activity.